Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations ( ∼ 347 µatm fCO2) up to values projected for the year 2100 ( ∼ 1333 µatm fCO2). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO2. Although this coastal plankton community was tolerant of high pCO2 levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.
Posts Tagged 'Baltic'
Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea (update)
Published 19 December 2016 Media coverage , Science ClosedTags: Baltic, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, physiology, phytoplankton
Highly sensitive poisoning-resistant optical carbon dioxide sensors for environmental monitoring
Published 16 December 2016 Science ClosedTags: Baltic, chemistry, field, methods
A new optical carbon dioxide sensor for marine applications is presented. It combines a robust and long-term stable sensing material with a compact read-out device. The sensing material relies on a NIR pH indicator immobilized into ethyl cellulose along with a quaternary ammonium base. The perfluorinated polymer Hyflon AD 60 used as a protection layer significantly enhances the long-term and mechanical stability of the sensor foils, as well as the robustness against poisoning gases, e.g. hydrogen sulfide. The sensor can be stored at ambient conditions for more than six weeks whereas sensors covered with silicone rubber deteriorate within one week under the same conditions. The complete sensor device is applicable after a three-point (re)calibration without a preconditioning step. The carbon dioxide production and consumption of the water plant Egeria densa was measured in the laboratory. Furthermore, results of profiling carbon dioxide measurements during a research cruise on the Baltic Sea at water depths up to 225 m are presented.
Performance of herring larvae in a simulated future ocean food web, using the “Kiel Off-Shore Mesocosms for future Ocean Simulations”
Published 13 December 2016 Science ClosedTags: Baltic, biological response, BRcommunity, communityMF, field, fish, mesocosms, morphology, multiple factors, performance, phytoplankton, reproduction
We studied the combined direct physiological and indirect food web effects of ocean acidification on herring larvae inside pelagic mesocosms. A natural plankton community of the Gullmarsfjord, Sweden was enclosed in the Kiel Off-Shore Mesocosms for future Ocean Simulations (KOSMOS) for 113 days from March to June 2013 at ambient and projected end-of-the-century CO2 levels (~760 µatm pCO2). Herring eggs were introduced into the mesocosms, where they hatched in mid of May. The larvae developed inside the mesocosms for ~6 weeks, feeding on prey organisms that experienced treatment CO2 levels for ~9 weeks. This video is meant as an illustration of the herring larvae«s performance inside our mesocosm units.
Ocean acidification challenges copepod phenotypic plasticity (update)
Published 18 November 2016 Science ClosedTags: Baltic, biogeochemistry, biological response, crustaceans, field, mesocosms, morphology, physiology, reproduction, zooplankton
Ocean acidification is challenging phenotypic plasticity of individuals and populations. Calanoid copepods (zooplankton) are shown to be fairly plastic against altered pH conditions, and laboratory studies indicate that transgenerational effects are one mechanism behind this plasticity. We studied phenotypic plasticity of the copepod Acartia sp. in the course of a pelagic, large-volume mesocosm study that was conducted to investigate ecosystem and biogeochemical responses to ocean acidification. We measured copepod egg production rate, egg-hatching success, adult female size and adult female antioxidant capacity (ORAC) as a function of acidification (fCO2 ∼ 365–1231 µatm) and as a function of quantity and quality of their diet. We used an egg transplant experiment to reveal whether transgenerational effects can alleviate the possible negative effects of ocean acidification on offspring development. We found significant negative effects of ocean acidification on adult female size. In addition, we found signs of a possible threshold at high fCO2, above which adaptive maternal effects cannot alleviate the negative effects of acidification on egg-hatching and nauplii development. We did not find support for the hypothesis that insufficient food quantity (total particulate carbon < 55 µm) or quality (C : N) weakens the transgenerational effects. However, females with high-ORAC-produced eggs with high hatching success. Overall, these results indicate that Acartia sp. could be affected by projected near-future CO2 levels.
Continue reading ‘Ocean acidification challenges copepod phenotypic plasticity (update)’
Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment (update)
Published 7 November 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, field, mesocosms, morphology, otherprocess, phytoplankton, primary production, prokaryotes, respiration
About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient ( ∼ 370 µatm) to high ( ∼ 1200 µatm), were set up in mesocosm bags ( ∼ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ∼ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was ∼ 100 mmol C m−2 day−1, from which 75–95 % was respired, ∼ 1 % ended up in the TPC (including export), and 5–25 % was added to the DOC pool. During phase II, the respiration loss increased to ∼ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ∼ 30 % lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The “extra” organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.
Future warming and acidification effects on anti-fouling and anti-herbivory traits of the brown alga Fucus vesiculosus (Phaeophyceae)
Published 14 October 2016 Science ClosedTags: algae, Baltic, biological response, BRcommunity, field, mesocosms, multiple factors, otherprocess, temperature
Human induced ocean warming and acidification have received increasing attention over the past decade and are considered to have substantial consequences for a broad range of marine species and their interactions. Understanding how these interactions shift in response to climate change is particularly important with regard to foundation species, such as the brown alga Fucus vesiculosus. This macroalga represents the dominant habitat former on coastal rocky substrata of the Baltic Sea, fulfilling functions essential for the entire benthic community. Its ability to withstand extensive fouling and herbivory regulates the associated community and ecosystem dynamics. This study tested the interactive effects of future warming, acidification and seasonality on the interactions of a marine macroalga with potential foulers and consumers. F. vesiculosus rockweeds were exposed to different combinations of conditions predicted regionally for the year 2100 (+∆5°C, +∆700 μatm CO2) using multi-factorial long-term experiments in novel outdoor benthic mesocosms (‘Benthocosms’) over 9-12 week periods in four seasons. Possible shifts in the macroalgal susceptibility to fouling and consumption were tested using consecutive bioassays. Algal susceptibility to fouling and grazing varied substantially among seasons and between treatments. In all seasons, warming predominantly affected anti-fouling and anti-herbivory interactions while acidification had a subtle non-significant influence. Interestingly, anti-microfouling activity was highest during winter under warming, while anti-macrofouling and anti-herbivory activities were highest in the summer under warming. These contrasting findings indicate that seasonal changes in anti-fouling and anti-herbivory traits may interact with ocean warming in altering F. vesiculosus community composition in the future.
The effect of CO2 enrichment on net photosynthesis of the red alga Furcellaria lumbricalis in a brackish water environment
Published 11 October 2016 Science ClosedTags: algae, Baltic, biological response, chemistry, field, laboratory, light, mesocosms, multiple factors, nutrients, photosynthesis, primary production, temperature
Anthropogenic carbon dioxide (CO2) emissions to the atmosphere are causing reduction in the global ocean pH, also known as ocean acidification. This change alters the equilibrium of different forms of dissolved inorganic carbon in seawater that macroalgae use for their photosynthesis. In the Baltic Sea, benthic macroalgae live in a highly variable environment caused by seasonality and rapid changes in meteorological conditions. The effect of increasing water CO2 concentration on the net photosynthesis of the red macroalgae Furcellaria lumbricalis (Hudson) Lamouroux was tested in short-term mesocosm experiments conducted in Kõiguste Bay (N Gulf of Riga) in June–July 2012 and 2013. Separate mesocosms were maintained at different pCO2 levels: ca. 2,000, ca. 1,000 and ca. 200 µatm. In parallel, different environmental factors were measured such as nutrients, light and water temperature. Thus, the current study also investigated whether elevated pCO2 and different environmental factors exerted interactive effects on the photosynthetic rate of F. lumbricalis. In addition, laboratory experiments were carried out to determine the optimal temperature for photosynthesis of F. lumbricalis. The results of our field experiments demonstrated that elevated pCO2 levels may remarkably enhance the photosynthetic rate of F. lumbricalis. However, the magnitude of this effect is altered by different environmental factors, mainly by changes in water temperature.
Climate-driven change in a Baltic Sea summer microplanktonic community – desalination play a more important role than ocean acidification
Published 5 October 2016 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, chemistry, community composition, field, growth, morphology, otherprocess, photosynthesis, phytoplankton, primary production, prokaryotes
Scenario modeling suggests that the Baltic Sea, one of the largest brackish-water bodies in the world, could expect increased precipitation (decreased salinity) and increased concentration of atmospheric CO2 over the next 100 years. These changes are expected to affect the microplanktonic food web, and thereby nutrient and carbon cycling, in a complex and possibly synergistic manner. In the Baltic Proper, the extensive summer blooms dominated by the filamentous cyanobacteria Aphanizomenon sp., Dolichospermum sp. and the toxic Nodularia spumigena, contribute up to 30 % of the yearly new nitrogen and carbon exported to the sediment. In a 12 days outdoor microcosm experiment, we tested the combined effects of decreased salinity (from 6 to 3) and increased CO2 concentrations (380 and 960 µatm) on a natural summer microplanktonic community, focusing on diazotrophic filamentous cyanobacteria. Based on our results, the most important factor was salinity, and pCO2 showed only minor effects on total biovolumes of phytoplankton and abundances of heterotrophic bacteria. No interaction effects of salinity and pCO2 were found on any of the measured parameters. The biovolume of the toxic N. spumigena was negatively affected by salinity 3, and the treatment with salinity 3 and 960 µatm CO2 resulted in increased biomass of the presumably non-toxic Dolichospermum sp. Biovolumes of ciliates, diatoms and dinoflagellates were lower in salinity 3. Thus, the lower salinity seemed more important than increased pCO2, and considering the Baltic Proper, we do not expect any dramatic effects of increased pCO2 in combination with decreased salinity on the microplanktonic food web. We believe that our study can add one piece to the complicated puzzle to reveal the combined effects of increased pCO2 and reduced salinity levels on the Baltic microplanktonic community.
Warming and acidification effects on planktonic heterotrophic pico- and nanoflagellates in a mesocosm experiment
Published 16 September 2016 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, laboratory, mesocosms, multiple factors, otherprocess, performance, protists, temperature
We studied the response of the heterotrophic flagellate (HF) community to the combined impact of warming and ocean acidification in a mesocosm experiment with a plankton community from the western Baltic Sea. We performed a quantitative analysis of the response at the level of total biomass and size classes and a semi-quantitative one at the level of individual taxa. Total biomass of HF was significantly lower under higher temperatures while there was no significant effect of CO2. The mean biomass of the picoflagellates did not respond to temperature while the three nanoflagellate size classes (class limits 3, 5, 8, 15 μm) responded negatively to warming while not responding to CO2. The taxon-level results indicate that heterotrophic flagellates do not form a homogenous trophic guild, as often assumed in pelagic food web studies. Instead, the heterotrophic flagellates formed a “food web within the food web”. There was a pronounced succession of flagellates leading from a dominance of bacterivores and colloidal matter feeders before the phytoplankton bloom to omnivorous feeders preying upon phytoplankton and heterotrophic flagellates during and after the bloom. This complex intraguild predation patterns probably dampened the response to experimental treatments.
Ocean acidification effects on Atlantic cod larval survival and recruitment to the fished population
Published 24 August 2016 Science ClosedTags: Arctic, Baltic, biological response, communitymodeling, fish, fisheries, laboratory, modeling, mortality, reproduction
How fisheries will be impacted by climate change is far from understood. While some fish populations may be able to escape global warming via range shifts, they cannot escape ocean acidification (OA), an inevitable consequence of the dissolution of anthropogenic carbon dioxide (CO2) emissions in marine waters. How ocean acidification affects population dynamics of commercially important fish species is critical for adapting management practices of exploited fish populations. Ocean acidification has been shown to impair fish larvae’s sensory abilities, affect the morphology of otoliths, cause tissue damage and cause behavioural changes. Here, we obtain first experimental mortality estimates for Atlantic cod larvae under OA and incorporate these effects into recruitment models. End-of-century levels of ocean acidification (~1100 μatm according to the IPCC RCP 8.5) resulted in a doubling of daily mortality rates compared to present-day CO2 concentrations during the first 25 days post hatching (dph), a critical phase for population recruitment. These results were consistent under different feeding regimes, stocking densities and in two cod populations (Western Baltic and Barents Sea stock). When mortality data were included into Ricker-type stock-recruitment models, recruitment was reduced to an average of 8 and 24% of current recruitment for the two populations, respectively. Our results highlight the importance of including vulnerable early life stages when addressing effects of climate change on fish stocks.
Simulated leakage of high pCO2 water negatively impacts bivalve dominated infaunal communities from the Western Baltic Sea
Published 23 August 2016 Science ClosedTags: abundance, Baltic, biological response, BRcommunity, community composition, dissolution, laboratory, mesocosms, mitigation, mollusks, mortality, nematodes, otherprocess, prokaryotes, sediment
Carbon capture and storage is promoted as a mitigation method counteracting the increase of atmospheric CO2 levels. However, at this stage, environmental consequences of potential CO2 leakage from sub-seabed storage sites are still largely unknown. In a 3-month-long mesocosm experiment, this study assessed the impact of elevated pCO2 levels (1,500 to 24,400 μatm) on Cerastoderma edule dominated benthic communities from the Baltic Sea. Mortality of C. edule was significantly increased in the highest treatment (24,400 μatm) and exceeded 50%. Furthermore, mortality of small size classes (0–1 cm) was significantly increased in treatment levels ≥6,600 μatm. First signs of external shell dissolution became visible at ≥1,500 μatm, holes were observed at >6,600 μatm. C. edule body condition decreased significantly at all treatment levels (1,500–24,400 μatm). Dominant meiofauna taxa remained unaffected in abundance. Densities of calcifying meiofauna taxa (i.e. Gastropoda and Ostracoda) decreased in high CO2 treatments (>6,600 μatm), while the non – calcifying Gastrotricha significantly increased in abundance at 24,400 μatm. In addition, microbial community composition was altered at the highest pCO2 level. We conclude that strong CO2 leakage can alter benthic infauna community composition at multiple trophic levels, likely due to high mortality of the dominant macrofauna species C. edule.
Ocean acidification decreases plankton respiration: evidence from a mesocosm experiment (update)
Published 23 August 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, crustaceans, field, mesocosms, otherprocess, phytoplankton, primary production, prokaryotes, respiration, zooplankton
Anthropogenic carbon dioxide (CO2) emissions are reducing the pH in the world’s oceans. The plankton community is a key component driving biogeochemical fluxes, and the effect of increased CO2 on plankton is critical for understanding the ramifications of ocean acidification on global carbon fluxes. We determined the plankton community composition and measured primary production, respiration rates and carbon export (defined here as carbon sinking out of a shallow, coastal area) during an ocean acidification experiment. Mesocosms ( ∼ 55 m3) were set up in the Baltic Sea with a gradient of CO2 levels initially ranging from ambient ( ∼ 240 µatm), used as control, to high CO2 (up to ∼ 1330 µatm). The phytoplankton community was dominated by dinoflagellates, diatoms, cyanobacteria and chlorophytes, and the zooplankton community by protozoans, heterotrophic dinoflagellates and cladocerans. The plankton community composition was relatively homogenous between treatments. Community respiration rates were lower at high CO2 levels. The carbon-normalized respiration was approximately 40 % lower in the high-CO2 environment compared with the controls during the latter phase of the experiment. We did not, however, detect any effect of increased CO2 on primary production. This could be due to measurement uncertainty, as the measured total particular carbon (TPC) and combined results presented in this special issue suggest that the reduced respiration rate translated into higher net carbon fixation. The percent carbon derived from microscopy counts (both phyto- and zooplankton), of the measured total particular carbon (TPC), decreased from ∼ 26 % at t0 to ∼ 8 % at t31, probably driven by a shift towards smaller plankton (< 4 µm) not enumerated by microscopy. Our results suggest that reduced respiration leads to increased net carbon fixation at high CO2. However, the increased primary production did not translate into increased carbon export, and consequently did not work as a negative feedback mechanism for increasing atmospheric CO2 concentration.
Effect of ocean acidification and elevated fCO2 on trace gas production by a Baltic Sea summer phytoplankton community (update)
Published 16 August 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, community composition, field, mesocosms, otherprocess, phytoplankton, prokaryotes
The Baltic Sea is a unique environment as the largest body of brackish water in the world. Acidification of the surface oceans due to absorption of anthropogenic CO2 emissions is an additional stressor facing the pelagic community of the already challenging Baltic Sea. To investigate its impact on trace gas biogeochemistry, a large-scale mesocosm experiment was performed off Tvärminne Research Station, Finland, in summer 2012. During the second half of the experiment, dimethylsulfide (DMS) concentrations in the highest-fCO2 mesocosms (1075–1333 µatm) were 34 % lower than at ambient CO2 (350 µatm). However, the net production (as measured by concentration change) of seven halocarbons analysed was not significantly affected by even the highest CO2 levels after 5 weeks’ exposure. Methyl iodide (CH3I) and diiodomethane (CH2I2) showed 15 and 57 % increases in mean mesocosm concentration (3.8 ± 0.6 increasing to 4.3 ± 0.4 pmol L−1 and 87.4 ± 14.9 increasing to 134.4 ± 24.1 pmol L−1 respectively) during Phase II of the experiment, which were unrelated to CO2 and corresponded to 30 % lower Chl a concentrations compared to Phase I. No other iodocarbons increased or showed a peak, with mean chloroiodomethane (CH2ClI) concentrations measured at 5.3 (±0.9) pmol L−1 and iodoethane (C2H5I) at 0.5 (±0.1) pmol L−1. Of the concentrations of bromoform (CHBr3; mean 88.1 ± 13.2 pmol L−1), dibromomethane (CH2Br2; mean 5.3 ± 0.8 pmol L−1), and dibromochloromethane (CHBr2Cl, mean 3.0 ± 0.5 pmol L−1), only CH2Br2 showed a decrease of 17 % between Phases I and II, with CHBr3 and CHBr2Cl showing similar mean concentrations in both phases. Outside the mesocosms, an upwelling event was responsible for bringing colder, high-CO2, low-pH water to the surface starting on day t16 of the experiment; this variable CO2 system with frequent upwelling events implies that the community of the Baltic Sea is acclimated to regular significant declines in pH caused by up to 800 µatm fCO2. After this upwelling, DMS concentrations declined, but halocarbon concentrations remained similar or increased compared to measurements prior to the change in conditions. Based on our findings, with future acidification of Baltic Sea waters, biogenic halocarbon emissions are likely to remain at similar values to today; however, emissions of biogenic sulfur could significantly decrease in this region.
No observed effect of ocean acidification on nitrogen biogeochemistry in a summer Baltic Sea plankton community (update)
Published 8 July 2016 Science ClosedTags: abundance, Baltic, biogeochemistry, biological response, BRcommunity, field, mesocosms, nitrogen fixation, otherprocess, prokaryotes
Nitrogen fixation by filamentous cyanobacteria supplies significant amounts of new nitrogen (N) to the Baltic Sea. This balances N loss processes such as denitrification and anammox, and forms an important N source supporting primary and secondary production in N-limited post-spring bloom plankton communities. Laboratory studies suggest that filamentous diazotrophic cyanobacteria growth and N2-fixation rates are sensitive to ocean acidification, with potential implications for new N supply to the Baltic Sea. In this study, our aim was to assess the effect of ocean acidification on diazotroph growth and activity as well as the contribution of diazotrophically fixed N to N supply in a natural plankton assemblage. We enclosed a natural plankton community in a summer season in the Baltic Sea near the entrance to the Gulf of Finland in six large-scale mesocosms (volume ∼ 55 m3) and manipulated fCO2 over a range relevant for projected ocean acidification by the end of this century (average treatment fCO2: 365–1231 µatm). The direct response of diazotroph growth and activity was followed in the mesocosms over a 47 day study period during N-limited growth in the summer plankton community. Diazotrophic filamentous cyanobacteria abundance throughout the study period and N2-fixation rates (determined only until day 21 due to subsequent use of contaminated commercial 15N-N2 gas stocks) remained low. Thus estimated new N inputs from diazotrophy were too low to relieve N limitation and stimulate a summer phytoplankton bloom. Instead, regeneration of organic N sources likely sustained growth in the plankton community. We could not detect significant CO2-related differences in neither inorganic nor organic N pool sizes, or particulate matter N : P stoichiometry. Additionally, no significant effect of elevated CO2 on diazotroph activity was observed. Therefore, ocean acidification had no observable impact on N cycling or biogeochemistry in this N-limited, post-spring bloom plankton assemblage in the Baltic Sea.
Long-term alkalinity trends in the Baltic Sea and their implications for CO2-induced acidification
Published 6 July 2016 Science ClosedTags: Baltic, chemistry, review
Currently, around 30% of anthropogenic CO2 emissions are taken up by the oceans (Le Quéré et al., 2015). This mitigates rising atmospheric CO2 levels, but comes at the price of decreasing seawater pH. On multi-millennial time scales intensified continental weathering is expected to contribute to increasing oceanic alkalinity (AT). Because AT neutralizes a large share of the protons that are produced by the dissolution of CO2 in seawater, rising AT concentrations would increase the oceans storage capacity for CO2 and mitigate the acidification signal (Lenton and Britton, 2006). The Baltic Sea is an ideal study site for such AT dynamics, due to its direct link to terrestrial processes, short water residence time and long history of AT measurements dating back to the early 20th century. (…)
Peculiarities of the Baltic Sea acid-base system
Published 6 July 2016 Science ClosedTags: Baltic, biogeochemistry, chemistry, review
There is a general belief that the magnitude of ocean acidification can sufficiently be quantified from the atmospheric pCO2 levels and the CO2 exchange between seawater and the atmosphere. This is approximately true for oceanic waters. However, it is not the case for coastal seas because several other processes and mechanisms are influencing the seawater pH. These form the so called acid-base system – a complex net of interrelationships between chemical species and processes that control the seawater pH. At present, the knowledge on the structure and functioning of the acid-base system contains a lot of gaps and/or shortcomings, which lead to wrong conclusions and questionable predictions of the future pH development. Since the CO2 system is an integral part of the acid-base system, it is impossible to understand the CO2 system and to assess processes such as the CO2 gas exchange or calcium carbonate dissolution/formation, without a clear
idea about the structure and functioning of the whole acid-base system. In this context the Baltic Sea can be considered as a test field because on one hand the low buffer capacity makes the Baltic Sea vulnerable to acidification, and on the other hand the sea is exposed to various anthropogenic influences which have the potential to change the acid-base system.
Continue reading ‘Peculiarities of the Baltic Sea acid-base system’
Survival and settling of larval Macoma balthica in a large-scale mesocosm experiment at different fCO2 levels (update)
Published 10 June 2016 Science ClosedTags: Baltic, biological response, field, mesocosms, mollusks, morphology, reproduction
Anthropogenic carbon dioxide (CO2) emissions are causing severe changes in the global inorganic carbon balance of the oceans. Associated ocean acidification is expected to pose a major threat to marine ecosystems worldwide, and it is also expected to be amplified in the Baltic Sea where the system is already exposed to relatively large natural seasonal and diel pH fluctuations. We studied the responses of larvae of the benthic key species Macoma balthica to a range of future CO2 scenarios using six ∼ 55 m3 mesocosms encompassing the entire pelagic community. The mesocosms were deployed in the northern Baltic Sea in June 2012. We focused on the survival, growth and subsequent settlement process of Macoma balthica when exposed to different levels of future CO2. The size and time to settlement of M. balthica increased along the CO2 gradient, suggesting a developmental delay. With ongoing climate change, both the frequency and extent of regularly occurring high CO2 conditions are likely to increase, and a permanent pH decrease will likely occur. The strong impact of increasing CO2 levels on early-stage bivalves is alarming as these stages are crucial for sustaining viable populations, and a failure in their recruitment would ultimately lead to negative effects on the population.
Impact of high pCO2 on shell structure of the bivalve Cerastoderma edule
Published 6 June 2016 Science ClosedTags: Baltic, biological response, dissolution, field, laboratory, mollusks, morphology, North Atlantic
Raised atmospheric emissions of carbon dioxide (CO2) result in an increased ocean pCO2 level and decreased carbonate saturation state. Ocean acidification potentially represents a major threat to calcifying organisms, specifically mollusks. The present study focuses on the impact of elevated pCO2 on shell microstructural and mechanical properties of the bivalve Cerastoderma edule. The mollusks were collected from the Baltic Sea and kept in flow-through systems at six different pCO2 levels from 900 μatm (control) to 24,400 μatm. Extreme pCO2 levels were used to determine the effects of potential leaks from the carbon capture and sequestration sites where CO2 is stored in sub-seabed geological formations. Two approaches were combined to determine the effects of the acidified conditions: (1) Shell microstructures and dissolution damage were analyzed using scanning electron microscopy (SEM) and (2) shell hardness was tested using nanoindentation. Microstructures of specimens reared at different pCO2 levels do not show significant changes in their size and shape. Likewise, the increase of pCO2 does not affect shell hardness. However, dissolution of ontogenetically younger portions of the shell becomes more severe with the increase of pCO2. Irrespective of pCO2, strong negative correlations exist between microstructure size and shell mechanics. An additional sample from the North Sea revealed the same microstructural-mechanical interdependency as the shells from the Baltic Sea. Our findings suggest that the skeletal structure of C. edule is not intensely influenced by pCO2 variations. Furthermore, our study indicates that naturally occurring shell mechanical property depends on the shell architecture at μm-scale.
Continue reading ‘Impact of high pCO2 on shell structure of the bivalve Cerastoderma edule’
Combined effects of ocean warming and acidification on copepod abundance, body size and fatty acid content
Published 26 May 2016 Science ClosedTags: abundance, Baltic, biological response, crustaceans, laboratory, mesocosms, morphology, multiple factors, otherprocess, physiology, temperature, zooplankton
Concerns about increasing atmospheric CO2 concentrations and global warming have initiated studies on the consequences of multiple-stressor interactions on marine organisms and ecosystems. We present a fully-crossed factorial mesocosm study and assess how warming and acidification affect the abundance, body size, and fatty acid composition of copepods as a measure of nutritional quality. The experimental set-up allowed us to determine whether the effects of warming and acidification act additively, synergistically, or antagonistically on the abundance, body size, and fatty acid content of copepods, a major group of lower level consumers in marine food webs. Copepodite (developmental stages 1–5) and nauplii abundance were antagonistically affected by warming and acidification. Higher temperature decreased copepodite and nauplii abundance, while acidification partially compensated for the temperature effect. The abundance of adult copepods was negatively affected by warming. The prosome length of copepods was significantly reduced by warming, and the interaction of warming and CO2 antagonistically affected prosome length. Fatty acid composition was also significantly affected by warming. The content of saturated fatty acids increased, and the ratios of the polyunsaturated essential fatty acids docosahexaenoic- (DHA) and arachidonic acid (ARA) to total fatty acid content increased with higher temperatures. Additionally, here was a significant additive interaction effect of both parameters on arachidonic acid. Our results indicate that in a future ocean scenario, acidification might partially counteract some observed effects of increased temperature on zooplankton, while adding to others. These may be results of a fertilizing effect on phytoplankton as a copepod food source. In summary, copepod populations will be more strongly affected by warming rather than by acidifying oceans, but ocean acidification effects can modify some temperature impacts.
Effects of CO2 perturbation on phosphorus pool sizes and uptake in a mesocosm experiment during a low productive summer season in the northern Baltic Sea (update)
Published 25 May 2016 Science ClosedTags: Baltic, chemistry, field, mesocosms
Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26 ± 0.03 and 0.23 ± 0.04 µmol L−1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15 ± 0.02 in the mesocosms and 0.17 ± 0.07 µmol L−1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82 % of PO4 was converted into DOP whereby only 18 % of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9 nmol L−1 h−1. About 86 % of them was realized by the size fraction < 3 µm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27 % of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments > 1000 µatm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO2 conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.
